Small-sized catheters (27 to 32G) are needed in ever-increasing numbers for use, for example, in a continuous spinal anesthesia in the field of regional anesthesia--and not only for anesthesia but also for analgesic purposes.
A catheter unit of the type mentioned can be seen in DE 38 18 431 C1. In this instance the catheter unit consists of a small epidural tube which has an adjustable puncturing element whose point extends beyond the front end of the epidural tube in the interposed position. The tube itself is blunt and without a cutting surface. The puncturing element involves a trocar, which in the interposed position extends beyond the front end of the tube solely with its full point.
Because of the construction of the tube and especially because of its blunt rim, which produces a relatively large cross section, it is essentially impossible to guarantee that the fibers of the dura mater will not be damaged.
A steel tubule for spinal and peridural anesthesia is described in DE 36 43 235 C1. A conical-elliptical tubule has a slope which leads to a lateral opening of the tubule, so as in this way to guide a catheter along the slope through the opening to the outside. Such a design has the disadvantage of making it very difficult for a small-sized, thin-walled catheter to overcome the resistance of the slope. As a result, the catheter has to be equipped with a strong mandrin, which necessarily increases the risk of trauma. It can also be seen that the mandrin can be clamped on the slope in the catheter so that further movement is linked to a simultaneous movement of the tubule. By this means, however, there is still a risk of injury.
A double tubule for peridural anesthesia is known from DE 32 18 242 C2. In this case, the outer tubule is the puncturing tubule and has a sharp, open point.
According to DE 87 15 740 U1, a combination needle for axillary plexus-brachialis anesthesia consists of an inner tubule with a bulgy, cone-shaped stopper which can be soldered, glued or pressed into the tubule.